In an optical router the information that passes through the core switching fabric is a chunk of information that must go from the input side of a line shelf through the optical switch itself to the egress side of a switch shelf. No storage is available in the optical switch itself. Therefore the information must be formatted in such a way that data passes through the optical switch and is collected on the egress side, such that every chunk that is collected can potentially require a different phase adjustment for clock and data recovery. Further, since the chunk size is significantly larger than the minimum size packet that is brought into the system, there needs to be a more efficient method to transfer small packets through the optical switch itself.
An optical system exhibits cross-talk and relatively high loss characteristics. Thus, errors that are incurred through the optical switch require error checking and correcting for a high degree of reliability. To pick a given chunk out of a stream of random bits requires framing information. Additionally, it is required to have a reasonably equal mix of zeroes and ones with reasonable limitation of continuous streams of zeroes and ones for DC balance going through the optical switch, resulting in DC balance of light coming into the optical receiving circuitry from the switch itself.